1. Field of the Invention
The present invention is directed to an instrument that monitors the composition of a vapor. More specifically, the present invention is directed to an instrument that in situ monitors for vapor phase polycyclic aromatic hydrocarbons in a burning cigarette.
2. Background Information
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Polyaromatic hydrocarbons (PAHs) are a large class of multi-ring structures that contain carbon and hydrogen atoms. These compounds are environmentally and biologically important and originate from a wide variety of natural and anthropogenic sources. For example, a PAH can be generated by the incomplete combustion or pyrolysis of organic matter. Several of the more prevalent formation sources for PAHs include combustion, catalytic cracking of petroleum products and coal coking. Each of these processes occurs at various temperatures and under various environmental conditions, therefore leading to the formation of different PAHs.
Extensive research in the field of high-temperature fluorescence measurements of PAHs has occurred in the field of combustion analysis. Due to the great number of applications of combustion in our daily lives (e.g., heating, cooking, cigarette smoking, and so forth), PAHs are formed in great abundance in fuel rich combustion environments. These fuel rich environments can allow the PAH to escape further combustion and thus be released. Emitted PAHs generally adsorb on the surface of soot particles, thus allowing the dispersion of these compounds throughout the environment. Through the use of techniques such as fluorescence spectroscopy and hyperspectral fluorescence imaging, these species can be monitored during simple, controlled combustion reactions. However, due to the difficulties associated with identification of a specific species (because of spectral shifts, line broadening and spectral overlap), high-temperature fluorescence measurements are often used to provide a qualitative proof of the general presence of PAHs but not in the identification of the specific species being measured.
Several procedures are known for obtaining compound specific information for evaluation of PAH contamination. However, additional sample preparation steps of collection and extraction make real time or in-situ measurements impossible. For example, gas chromatography/mass spectrometry (GCMS) has previously been used to detect the presence of PAHs. Analysis of PAHs by GCMS requires the prior collection of suspected PAH containing material and extraction of the PAH with solvents (such as methanol). Additionally, GCMS methods, in particular, are complicated, time consuming, and expensive, requiring significant resources such as high-vacuum equipment and extensive investment in highly trained personnel. Further, it is not cost-effective to apply previous PAH analysis techniques routinely to samples that may not, in fact, contain any relevant levels of PAH. Moreover, GCMS methods and similar techniques are not adaptable to in-situ environments in which vapor-phase analysis is to be conducted nor can GCMS be used for fast feedback which can be required for both environmental protection and for industrial process control.
Common forms of real-time analysis procedures utilize optical spectroscopy and, more particularly, fluorescence analysis. This is due to the inherent sensitivity of the technique and the great number of methods that have been developed over the years for differentiation of fluorescence signals from the intense background emissions often present at high temperatures. Other techniques include time-resolved fluorescence and hyperspectral fluorescence imaging. A more complete treatment of known methods in PAH analysis can be found in Brian M. Cullum et al., High-Temperature Fluorescence Measurements and Instrumentation for Polyaromatic Hydrocarbons (PAH): A Review, Journal of Polycyclic Aromatic Compounds, Vol. 18, No. 1, p. 25 (2000), the entire contents of which are herein incorporated by reference.
Although several procedures are available to analyze PAHs, the ability to provide in situ analysis of a PAH in the vapor phase is very limited. For example, U.S. Pat. No. 5,880,830, discloses a method to detect PAHs. The method analyzes aerosols by depositing particles on a substrate or filter and subsequently using ultraviolet light spectroscopy methods to detect the presence of a PAH.
In evaluating PAHs in combustion environments, it would be desirable to monitor the combustion products for PAH content in real time and in situ. For example, in the evaluation of burning cigarettes, PAHs, which have a very low volatility, are generally combined with smoke particles (TPMs). The analysis of these products requires the chemical analysis of TPM which is lengthy and tedious. In addition, locating regions in a cigarette where PAH production occurs is currently not practical but could be of interest in product development. However, in-situ monitoring inside a combusting material is difficult because the temperatures encountered in burning environments, such as a cigarette, can be on the order of about 500xc2x0 C. or higher.
The monitoring and chemical analysis of PAHs is of interest to both environmental and toxicological scientists and the real-time detection and characterization of PAHs, including PAHs in vapor phases, during the combustion processes, such as the combustion of tobacco, would be desirable to facilitate a better understanding of the smoke formation process and the development of new products with less PAH production.
A monitoring apparatus for one or more vapor phase polycyclic aromatic hydrocarbons (PAHs) in a high-temperature environment has an excitation source producing electromagnetic radiation, an optical path having at least a first optical probe that optically communicates the electromagnetic radiation received at a proximal end to a distal end such that the electromagnetic radiation interacts with at least one vapor phase polycyclic aromatic hydrocarbon produced by a material undergoing combustion and produces at least one emitted wavelength of radiation characteristic of the at least one vapor phase polycyclic aromatic hydrocarbon. A positioner is coupled to the optical path and can slidably move the distal end of the first optical probe to maintain the distal end position at a desired position with respect to an area of the material undergoing combustion. In a single optical probe 180xc2x0 backscattered configuration, the first optical probe receives the radiation at at least one emitted wavelength at the distal end and optically communicates the radiation from the distal end of the first optical probe to the proximal end thereof such that the wavelength of radiation is received by a wavelength separator in optical communication therewith and operatively connected to a detector. The optical path can have an optional second optical probe and can be arranged in a dual optical probe 180xc2x0 backscattered configuration or in a dual optical probe 90xc2x0 side scattered configuration and in which the second optical probe receives the radiation at at least one emitted wavelength emitted from the vapor phase PAH and directs the radiation to a wavelength separator operatively connected to a detector. The wavelength separator can be a spectrometer or a monochromator and optional time-resolved detection capability can be provided by a trigger system.
In an additional embodiment, a vapor phase polycyclic aromatic hydrocarbon monitoring apparatus comprises means for generating electromagnetic radiation, means for directing the electromagnetic radiation to a gaseous by-product produced by a material undergoing combustion, and means for receiving emitted radiation from the material undergoing combustion having at least one wavelength characteristic of a polycyclic aromatic hydrocarbon and directing the emitted radiation to a detecting means. The means for directing the electromagnetic radiation and/or the means for receiving the emitted radiation is positionable to be co-located with the sample. The monitoring apparatus can further comprise a means for analyzing the emitted radiation from the material undergoing combustion and a means for time resolving the monitoring apparatus.
A method of monitoring at least one vapor phase PAH by detecting electromagnetic radiation is provided having the steps of producing electromagnetic radiation, directing the electromagnetic radiation along a first optical probe, positioning a distal end of the first optical probe with respect to an area containing gaseous by-products of a material undergoing combustion, interacting at least a portion of the produced electromagnetic radiation with the gaseous by-products to produce emitted radiation characteristic of at least one PAH, and monitoring the emitted radiation. Monitoring can be directing the emitted radiation to a wavelength separator using either the first optical probe or a second optical probe. The positioning locates the distal end of the first optical probe substantially co-located outside an area of the material undergoing combustion, within a combustion zone of a material undergoing combustion, or within an area of the material undergoing combustion outside the combustion zone and detecting a vapor phase polycyclic aromatic hydrocarbon.